The present invention relates in general to electrical motors, and more particularly, to a controller for a switched reluctance motor (SRM) as well as to a method to control this motor.
SRMs are brushless electrical motors; while the stator has windings (or xe2x80x9ccoilsxe2x80x9d) on each pole, the rotor does not have windings. Stator pole coils that are electrically connected in series or in parallel form a so-called phase winding (hereinafter xe2x80x9cphasexe2x80x9d). As illustrated, each pair of diametrically opposite coils is connected, but this is not essential. Ideally, magnetic flux entering the rotor from one stator pole balances the flux entering the rotor from the diametrically opposite stator pole, so that there is no mutual magnetic coupling among the phases.
A controller switches the phases in a predetermined sequence that is synchronized with the angular position of the rotor relative to the stator (hereinafter the position). Knowledge of the position of the rotor relative to the stator (xe2x80x9cshaft anglexe2x80x9d) is desired at any time of operation, and especially desired when the controller initiates the rotation of the rotor during the so-called xe2x80x9cstart-upxe2x80x9d. Starting-up reliability is of premium importance.
Various methods are known in the art that address the start-up scenario; often the position is measured and position information is fed into the controller. Position measurement is performed with specially dedicated position sensors or without them (xe2x80x9csensorlessxe2x80x9d). Measurement can comprise the estimation of magnetic flux, phase inductance, phase current in an energized phase or in a de-energized phase, or the measurement of other physical quantities. As with each measurement, inaccuracies are contributed to, for example, the phase resistance, the ambient and phase temperatures, static fiction between rotor and stator and other factors.
For the design of SRMs, the following references are useful: U.S. Pat. No. 5,955,861 (Jeoung et al.), U.S. Pat. No. 5,793,179 (Watkins), U.S. Pat. No. 5,325,026 (Lyons et al.), U.S. Pat. No. 5,107,195 (Lyons et al.), U.S. Pat. No. 5,097,190 (Lyons et al.), U.S. Pat. No. 4,933,620 (MacMinn), U.S. Pat. No. 4,642,543 (MacMinn).
The present invention seeks to provide an improved controller as well as a method for controlling the SRM.